The understanding of irradiation-induced strengthening in ferritic-martensitic high-Cr steels remains an essential issue in the assessment of materials for fusion and next generation fission reactors. Recent advanced experimental studies revealed the importance of solute-rich clusters, containing Cr, Ni, Si, P and Mn, which often are created as a consequence of segregation at dislocation lines. In this work, Metropolis Monte Carlo (MMC) is applied to investigate segregation of Cr and Ni atoms around edge dislocation lines in bcc Fe. The content of Cr is varied between 7% and 10%, with and without 0.25% of Ni. Molecular dynamics has subsequently been applied to the enriched dislocation lines to study the critical resolved shear stress at 300 K and 600 K for different concentrations of solutes in the alloy. It is found that even small amounts of Ni significantly increase the hardening of the material.